The present invention relates to anchors providing fixing to dense concrete, masonry and the like, the anchor being secured in a hole bored for its reception in a mass of dense concrete, masonry or the like.
Anchors are known in the form of a threaded bolt provided with an expandible sleeve which is placed in a pre-prepared bore and the sleeve expanded in the bore by drawing up the bolt by a threaded nut. Many forms of such sleeve anchors have been proposed and used, and it has been proposed, for example, to provide enhanced performance by providing a very large expansion of the sleeve. It has also been proposed to use such anchors in bores formed with various undercuts, particularly to improve the efficiencies of anchors subjected to tensile loads.
It has also been proposed to secure anchors, screw or plugs in soft materials which are provided with an external cutting means such as a screw thread which can produce undercutting by rotation of the anchor or plug when inserting it into the pre-prepared bore, but it has not been possible to use these in dense materials such as concrete.
It has also been proposed to use anchors in the form of a headed screw which is driven into a hole in concrete or masonry.
To date, however, none of these anchors have yet been able to reach required minimum performance standards for example in the compressive and tensile zones of concrete and still less the higher standards now proposed for minimum performance in tensile zones of concrete.